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Oil Analysis


Roger Lee

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Hi All,

 

To qualify for the extended 2000 hr. TBO you are supposed to do oil analysis. You should also do one even if you don't qualify. It is your early warning system to abnormal problems that you may not see. You don't need to do them at every 50 hr. oil change, but should do them at your 100 hr. inspection or every other oil change. They will never look the same as the values will change from one analysis to the other, but they should be within normal limits. Here is one of mine just to look at. Your values will be different. You will notice that if the values are normal they are highlighted in green. If they are suspicious and you need to take a close look at the next analysis then it is highlighted yellow. If you are in any danger of a problem it will be highlighted in red and the lab will call you. Each sample you send in is tested three times for an accurate reading if you send it to Avlabs. I know nothing of the other labs.

Roger\'s 600 hr. oil anaylisis 7-2010.pdf

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  • 2 weeks later...

Hi Markus,

 

As you do more and more analysis you will find that they change constantly. Some areas will go way up then way down the next time. All areas will constantly fluctuate. All you care about is the trends over time. If a certain area keeps going up and up and then into the yellow warning area or higher then it's time to really take notice and watch the next analysis even closer. I have seen some 912 owners that have fuel reported in their analysis. The oil analysis will fluctuate for many reasons, type of oil used, fuel used, long exposure to a humid environment, fuel with or with out ethanol, rpms (high verses low) used at normal cruise, ect.... These are just a few reasons why my oil analysis will never look just like the other persons and will constantly fluctuate. Using 100LL will cause lead to be higher and when I travel I like everybody else is stuck using 100LL. My main fuel is 91 oct. with ethanol approx. 95% of the time and if i have to use 100LL I always use the fuel additive Decalin to help keep the lead build up to an absolute minimum. Running a higher than normal rpm like 5300 or more at cruise will also help keep leading down. Low cruise rpms will cause a little more lead to deposit. Avlabs test each sample sent to them 3 times to get a balanced test and all you really care about is that the results are in the green area.

 

 

Okay here is the extra credit test question for today:

Does anyone know what happens to the lead when using 100LL and it mixes with a little moisture either from water in the oil or engine and usually just comes from the humidity after shutdown that enters through the air intake or exhaust? There is a chemical formed. What is the chemical?

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Hi Markus,

 

As you do more and more analysis you will find that they change constantly. Some areas will go way up then way down the next time. All areas will constantly fluctuate. All you care about is the trends over time. If a certain area keeps going up and up and then into the yellow warning area or higher then it's time to really take notice and watch the next analysis even closer. I have seen some 912 owners that have fuel reported in their analysis. The oil analysis will fluctuate for many reasons, type of oil used, fuel used, long exposure to a humid environment, fuel with or with out ethanol, rpms (high verses low) used at normal cruise, ect.... These are just a few reasons why my oil analysis will never look just like the other persons and will constantly fluctuate. Using 100LL will cause lead to be higher and when I travel I like everybody else is stuck using 100LL. My main fuel is 91 oct. with ethanol approx. 95% of the time and if i have to use 100LL I always use the fuel additive Decalin to help keep the lead build up to an absolute minimum. Running a higher than normal rpm like 5300 or more at cruise will also help keep leading down. Low cruise rpms will cause a little more lead to deposit. Avlabs test each sample sent to them 3 times to get a balanced test and all you really care about is that the results are in the green area.

 

 

Okay here is the extra credit test question for today:

Does anyone know what happens to the lead when using 100LL and it mixes with a little moisture either from water in the oil or engine and usually just comes from the humidity after shutdown that enters through the air intake or exhaust? There is a chemical formed. What is the chemical?

 

This is a little outside my expertise. Solid lead particles wouldn't react with water but may oxidize ("rust"). I believe 100LL has lead in solution. IF you could react lead with water, the expected product would be lead (II) hydroxide. A quick Wikipedia search shows some carbonate compounds often forming where Pb(OH)2 is expected. The relavant Wikipedia quotation is: "Lead(II) hydroxide, Pb(OH)2, is a hydroxide of lead, with lead in oxidation state +2. Although it appears a fundamentally simple compound, it is doubtful if lead hydroxide is stable as a solid phase. Lead basic carbonate (PbCO3·2Pb(OH)2) or lead(II) oxide (PbO) is encountered in practice where lead hydroxide is expected. This has been a subject of considerable confusion in the past." Hey, if a Chemist tells you it's confusing, BELIEVE HIM/HER!

 

Sorry, but that's the best I can do. The main thing I remember from lead chemistry was, IT'S VERY POISONOUS - DON'T USE IT!

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With the lead and the fuel burning we create sulfur dioxides and nitric acid compounds which produce corroding matter containing sulfuric acid and nitric acid in an exhaust gas passage. Internal combustion engines function by burning fuels (hydrocarbons) at high temperatures. In theory, the products of the combustion process are CO2 and water. It is not uncommon for incomplete combustion to occur which results in the formation of undesirable byproducts such as carbon monoxide, hydrocarbons and soot. Other reactions occurring in internal combustion engines include the oxidation on nitrogen molecules to produce nitrogen oxides and the oxidation of sulfur to form SO2 and a small percentage of SO3. Mix any of these compounds with the humidity that enters your engine through the air intake or the exhaust and you can form an acid compound on your valves and valve stems. In the Rotax classes they show some of these valves that are all pitted. As the engine cools it will draw in moist air if it's there. If I lived in some place very moist like the Northwest US or Florida I might be plugging my intake and exhaust after flying.

 

The answer I was looking for was an acidic compound.

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With the lead and the fuel burning we create sulfur dioxides and nitric acid compounds which produce corroding matter containing sulfuric acid and nitric acid in an exhaust gas passage. Internal combustion engines function by burning fuels (hydrocarbons) at high temperatures. In theory, the products of the combustion process are CO2 and water. It is not uncommon for incomplete combustion to occur which results in the formation of undesirable byproducts such as carbon monoxide, hydrocarbons and soot. Other reactions occurring in internal combustion engines include the oxidation on nitrogen molecules to produce nitrogen oxides and the oxidation of sulfur to form SO2 and a small percentage of SO3. Mix any of these compounds with the humidity that enters your engine through the air intake or the exhaust and you can form an acid compound on your valves and valve stems. In the Rotax classes they show some of these valves that are all pitted. As the engine cools it will draw in moist air if it's there. If I lived in some place very moist like the Northwest US or Florida I might be plugging my intake and exhaust after flying.

 

The answer I was looking for was an acidic compound.

 

OK Got it.

 

You are not going to get complete combustion in any regular combustion engine. If you get close, the engine will 'knock'. You need to have slightly more fuel than oxygen and will get some incomplete combustion. As stated above, soot and CO are the most common components of that combustion. Catalytic converters and other systems are used to ensure as complete combustion as possible and minimize these other compounds. However, this generally occurs in the exhaust system, not in the engine.

 

Sulphur dioxide and water will get you sulphurous acid (H2SO3). That's the same equation as "acid rain" and that would eat into and corrode metal over time. Fortunately, you shouldn’t see sulphuric acid (H2SO4). Sulphuric acid is a “strong acid” and would cause significantly more problems much quicker. Nitrous oxides (NO)x (there are always a large witch's brew of them, percentages depend on exact conditions) will often react similarly and form acidic compounds. So both sulphur and nitrogen oxides will react to make acidic compounds that can corrode metal.

Where I've seen these in action is automotive exhaust systems. Those that drive long distances get the whole system up to operating temperature and drive the moisture out of the system. Many short trips allow the acidic compounds to form, but do not allow the system to get hot enough the drive out the moisture. That’s why some mufflers can last 18 months and others five years. It's worst in the 'rust belt'. I wouldn’t think this would be a problem in aviation engines as they tend to run close to full power for long periods of time.

The only easy ways I know of minimizing in engine corrosion are: always run at operating temperatures for a reasonable amounts of time, make sure the engine has proper lubrication, and try to shut down without a lot of unburned fuel in the engine (e.g. don’t do a really big rev immediately before killing the engine).

I hope this helps. It’s not my area of expertise.

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Hi CRS123,

 

For us it isn't the running of the engine, but when they shut down and live in a humid climate and the moisture goes into the air intake and exhaust on a warm engine. The running of our Rotax does keep them cleaned out, but after the shut down is the problem time.When I was in Rotax school they even recommended plugs for these areas to prevent the moisture intrusion.

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Hi CRS123,

 

For us it isn't the running of the engine, but when they shut down and live in a humid climate and the moisture goes into the air intake and exhaust on a warm engine. The running of our Rotax does keep them cleaned out, but after the shut down is the problem time.When I was in Rotax school they even recommended plugs for these areas to prevent the moisture intrusion.

 

Hey Roger,

 

The plugs sound like a good idea. You could also try putting a drying agent (those little packages found in electronics boxes that say "Do Not Eat") with the plug. They should be able to soak up the moisture present and the plug should stop any new moisture getting in. Anything going near the exhaust will need to be very heat resistance. Common drying agents (desiccants) are Silica gel, calcium sulfate, & calcium chloride. I haven't had time to look up whether they would be suitable in an engine environment.

 

Cheers!

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